A two-wire phase control type dimmer using a phase control element such as a triac is widely used as a dimmer for incandescent bulbs. Therefore, if light from an LED can be controlled with use of the dimmer, a low-power type illumination system with a light control function can be conveniently realized only by exchanging light sources without renewing existing equipment and wiring. However, there actually exist the following problems.
(1) When the LED is lit at a low current level, no self-holding current of the phase control element of the dimmer can be secured, thereby causing flickering in the LED brightness. That is, in the case of lighting the LED at the same brightness, required self-holding current of the phase control element cannot be secured by current flowing in the LED since the current flowing in the LED is smaller than that flowing in an incandescent bulb.
(2) Although the dimmer includes a timer circuit having a time constant circuit for turning on the phase control element at a desired phase, operation current for operating the timer circuit cannot be supplied to the dimmer from the moment when an AC source is turned on. Therefore, the dimmer cannot be operated. Moreover, a converter for driving the LED is not activated in turning on the AC source and it takes time to activate the converter.
An LED lighting device is known which, in order to solve the above problems, includes a dynamic dummy load, which is arranged in parallel with a converter, receives a control signal from the converter and adjusts a load in response to the control signal, and thus makes self-holding current of a phase control element and operation current of a timer circuit of a dimmer flow when each of them is required.
However, an LC filter circuit or a resonant circuit, which is formed by a filter capacitor and a small inductor of an AC source line, inside the dimmer generates high-frequency vibration when the phase control element is turned on. Operation of a triac generally used as a phase control element is switched in switching of conduction and blocking in a manner that a conduction region on a chip is made large or small in accordance with a value and flowing time of current flowing through the chip in the element. When negative current of the high-frequency vibration flows for a short time and a peak value of the current is not smaller than a value of arc-extinguishing current inherent to the phase control element, the phase control element is not turned off. However, it has been understood that when the peak value of the negative current of the high-frequency vibration is smaller than the value of the arc-extinguishing current of the phase control element, required phase control cannot be performed. Regarding this problem, in the prior art, the dynamic dummy load exerts a damping effect to the high-frequency vibration to some extent, but the effect is insufficient.
Thereupon, it is considered that the high-frequency vibration is suppressed by inserting a damping resistor to an input end of the LED lighting device in series and operating the damping resistor as a load of the resonant circuit when current flows into the LED lighting device. A resistance value of the damping resistor is determined based on a resonance frequency of the resonant circuit or source voltage, and the high-frequency vibration is more effectively suppressed as consumption power of the damping resistor becomes larger. However, since the damping resistor is connected to a source line in series, power is constantly consumed during energization and thus a resistance value to be adopted in designing is limited due to heat generation or restriction to consumption power. Consequently, the damping effect to the high-frequency vibration when the phase control element is turned on becomes insufficient.
The present invention aims to provide an LED lighting device, which reduces heat generation and consumption power of a resistor of a damping circuit and has a dimmer capable of reliably operating, and an illumination apparatus including the LED lighting device.